1. Field of the Invention
The present invention relates to a crane vehicle comprising a telescopic boom which is hydraulically extensible by means of an assembly comprising a plunger cylinder. The boom can be extended by a derrick mast for enlarging the operating area of the crane.
2. Description of the Related Art
There is known a crane-vehicle which is provided with a telescopic boom that can be hydraulically extended by means of a plunger-cylinder assembly. Furthermore, it is known that the boom of the crane vehicle can be extended by means of a derrick mast for increasing the operative height of the crane. Different derrick masts are available for such a purpose. Derrick masts with large dimensions are produced as grid constructions which are anchored during operation. So far vehicle cranes with telescopic derrick masts have not been built.
As far as derrick masts are used on crane booms in the prior art, these are adjusted relative to the main boom with the help of ropes guided over at least one anchoring block. Said anchoring blocks form the point of action for the force that is e.g. required for lifting the derrick mast.
So far the experts have thought it technically impossible to provide a telescopic derrick mast in a vehicle crane. The reason for this assumption has to be seen in the fact that large amounts of hydraulic fluid have to be pumped upwards into the area of the derrick mast for telescopically extending a telescopic derrick mast on the one hand and for adjusting the inclination of a derrick mast on the other hand. To convey such large amounts of hydraulic fluid, flexible hoses for fluid media, which are known per se, must be provided with particularly large diameters. However, on account of the limited space on a crane vehicle, such large-dimensioned and long hoses for hydraulic media cannot be accommodated there.
A necessarily large hose diameter means that the hose in the wound state occupies a lot of space. However, since the storage space that is available on the crane vehicle for hoses is very limited, a further increase in the hose diameter is thus not possible. Furthermore, the small space that is available for wound hoses limits the hose length required for the extended crane system. Correspondingly large hose drums cannot be carried along on the crane vehicle, and a separate transportation by means of a trailer is excluded for economic reasons. A small hose diameter only allows the flow of small amounts of hydraulic fluid into the derrick mast, which makes it impossible to construct a hydraulically telescopic derrick mast of a satisfactory performance whose inclination is hydraulically adjustable. Furthermore, a hose system for the supply of hydraulic fluid to the derrick mast only allows for a limited length of the main boom because of the restricted hose length.
It is true that the drawback of the hose system, i.e. the derrick mast cannot be dimensioned in any desired way, can be avoided by using grid constructions as derrick masts. In such an instance, however, it must be accepted that grid constructions are not flexible and that their length is substantially unvariable after they have been mounted on the main boom. Furthermore, conventional derrick masts necessitate troublesome anchoring measures.
It is therefore the object of the present invention to provide a crane vehicle comprising a telescopic derrick mast of a hydraulically adjustable inclination and, in particular, to provide a supply line for hydraulic fluid which is capable of conveying the necessary large amounts of hydraulic fluid that are required for operating a derrick mast with large dimensions and a high load-bearing capacity.
This object is achieved in the case of a crane vehicle with a telescopic main boom [by the features indicated in the characterizing part of claim 1] in which a derrick mast can be telescoped hydraulically and a telescopic plunger cylinder of the main boom (20) is configured as a supply/discharge line for hydraulic fluid, the hydraulic fluid being adapted to be optionally supplied to a means for the telescopic extension of the derrick mast or to a derrick cylinder for hydraulically adjusting the inclination of the derrick mast.
The progress which can be achieved with the help of the invention is primarily due to the fact that neither an anchoring block nor a hydraulic fluid hose is needed for moving the derrick mast, i.e. for its telescopic movement and for the adjustment of its inclination. This advantage is due to the fact that thanks to the invention the large amounts of hydraulic fluid that are required for moving a telescopic derrick mast can be provided and pumped upwards to the derrick mast. Furthermore, the invention offers the advantage that the plunger cylinder of the main boom which is used as a supply line and discharge line, respectively, has an adequately large cross-sectional area through which large amounts of hydraulic fluid can flow. Moreover, the plunger cylinder is slid into itself while the boom is being retracted, so that in contrast to conventional hose supply systems an additional storage space is not needed. With respect to an advantageous space exploitation, the system of the invention is also superior to the conventional hose systems because of the combination of two functions in one component, as the plunger cylinder is firstly used for extending the boom and secondly as a supply line to the telescopic derrick mast. Thus an additional component, in this instance the hoses, can be dispensed with. In comparison with the conventional derrick masts designed as grid constructions, the hydraulically telescopic derrick mast of the invention can be handled more flexibly.
According to a preferred embodiment the derrick mast and also the derrick cylinder are detachably secured to the main boom.
Furthermore, according to a preferred embodiment of the present invention, it is possible that a telescopic inner tube is arranged within the plunger cylinder of the main boom. It is possible with the help of such an assembly to provide a hydraulic fluid circuit, for instance for a pump, in a compact form.
According to a further preferred embodiment of the present invention, lines which connect the plunger cylinder and the inner tube via a valve to a tank and a pump can be provided at the bottom end of the plunger cylinder. Advantageously, the arrangement of the tank and the pump at the bottom end of the plunger cylinder permits the combined use of the plunger cylinder as a device for extending the boom on the one hand and as a feed line to the derrick mast on the other hand.
According to another preferred embodiment of the present invention, lines can be provided at the upper end of the plunger cylinder for optionally connecting the plunger cylinder via valves either to the derrick mast or to the derrick cylinder. According to a further preferred embodiment of the present invention, the inner tube may serve as a pump return flow means and the space between inner tube and wall of the plunger cylinder as an advance flow means during extension while the derrick mast is operative.
Furthermore, according to a preferred embodiment the present invention, the inner tube may serve as a pump advance flow means during retraction of the derrick mast, and the space between inner tube and wall of the plunger cylinder as a pump return flow means.
Finally, according to a preferred embodiment of the present invention, the hydraulic medium may be a hydraulic oil.